Depending on how efficient they want to be, a bait bag could run anywhere from a single bit to two bytes per bait. Most likely one bit, 10 bits, or lazy mode two bytes. There's no need to carry item data beyond existence(extended to quantity in the second two options) because it can be an established list. "First value is lugworm. Second value is pillbug." etc. Options 2 and 3 would be for running a stack of up to 999 of the bait, while option 1 would require a method to buy/trade/whatever to unlock a permanent version of the bait.